The present invention relates to an apparatus for keeping open the gap cut by a saw in a work piece. More specifically, the invention relates to an apparatus for clamping a work piece in a metal saw, especially a circular metal saw.
Prior art clamping devices for clamping a work piece such as sectional steel in a saw are not entirely satisfactory for preventing that the gap formed by the advancing saw blade tends to become narrower as a result of tensions within the work piece which are released due to the formation of the saw blade gap. As soon as the saw blade has sufficiently advanced into a work piece, especially in the form of a large block, the released tension forces may narrow the saw blade gap to such an extent that the saw blade may be pinched by forces which can become large enough to exceed the drive power of the sawing apparatus, whereby the saw blade may be stopped altogether.
Our earlier U.S. Pat. No. 4,143,567 corresponding to German Pat. No. 2,641,255 describes an apparatus which aims at avoiding the above described problem. The clamping apparatus according to our earlier U.S. Pat. No. 4,143,567 comprises a rear clamping jaw or abutment member and two front clamping jaws arranged opposite the rear abutment member, but laterally spaced relative to a plane passing through the saw blade and through the rear abutment member. Each front clamping jaw is provided at its work engaging front face with edges or conical points. The front clamping jaws are displaced laterally relative to the saw blade in a slidable manner and against the force of strong biasing springs. The clamping jaws are operable by hydraulic piston cylinder means. Each of the two front clamping jaws has a supporting body with a slanting surface. The slant angle is within the range of 45.degree. to 75.degree. relative to the plane defined by the saw blade. The two slant angles for the two front clamping jaws are arranged mirror-symmetrically relative to the central plane defined by the saw blade. The work piece engaging portions of the front clamping jaws are pressed laterally apart in accordance with the geometric conditions established by the slant angles, whereby the spreading force components resulting from the clamping forces tend to move the clamping jaws axially outwardly away from the saw blade. As a result, the saw blade gap has a tendency to widen as the saw blade keeps advancing into the work piece. At least, the gap does not diminish in its width. When the two front clamping jaws are released, the spring members have a tendency to return the work piece engaging front portions of the jaws into a starting position.
The just described clamping apparatus according to U.S. Pat. No. 4,143,567 leaves room for improvement in the following respects. Due to the geometric arrangement of the slanting angles the spreading force component or rather components are determined by these angles and by the applied clamping force. Thus, the spreading force components which are derived from the clamping force, can be increased only by further increasing the clamping power which is directed perpendicularly to the longitudinal axis of the work piece. However, from a practical point of view the clamping power cannot be increased at random without becoming economically unfeasible.